Method and apparatus for transmitting and receiving reference signal in wireless communication system

ABSTRACT

Disclosed herein are a method and apparatus for performing, by UE, decoding in a wireless communication system. According to the present invention, there may be a method and an apparatus for decoding data in which a demodulation reference signal (DMRS) configured by a base station according to a specific pattern is received from the base station through a DMRS symbol, the demodulation reference signal is transmitted on a specific antenna port and located on the same one or two time-axis symbols as at least one other demodulation reference signal transmitted on another antenna port, the specific pattern is determined according to characteristics of a frequency band in which the demodulation reference signal is transmitted, the demodulation reference signal is mapped to the one or two time-axis symbols using at least one of a first code division multiplexing (CDM) on a frequency axis or a second CDM on a time axis, and the data are decoded using the demodulation reference signal.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method and an apparatus for generating andtransmitting and receiving a demodulation reference signal (DMRS) fordecoding data in a wireless communication system.

BACKGROUND ART

Mobile communication systems have been developed to provide voiceservices, while guaranteeing user activity. Service coverage of mobilecommunication systems, however, has extended even to data services, aswell as voice services, and currently, an explosive increase in traffichas resulted in shortage of resource and user demand for high speedservices, requiring advanced mobile communication systems.

The requirements of the next-generation mobile communication system mayinclude supporting huge data traffic, a remarkable increase in thetransfer rate of each user, the accommodation of a significantlyincreased number of connection devices, very low end-to-end latency, andhigh energy efficiency. To this end, various techniques, such as smallcell enhancement, dual connectivity, massive Multiple Input MultipleOutput (MIMO), in-band full duplex, non-orthogonal multiple access(NOMA), supporting super-wide band, and device networking, have beenresearched.

DISCLOSURE Technical Problem

An embodiment of the present invention provides a method and apparatusfor generating and transmitting and receiving a demodulation referencesignal (DMRS) for decoding data.

Furthermore, an embodiment of the present invention provides a methodand apparatus for generating and transmitting and receiving a DMRS forestimating common phase error (CPE)/carrier frequency offset (CFO)values due to a Doppler effect.

Furthermore, an embodiment of the present invention provides a mappingpattern of a demodulation reference signal in consideration of atrade-off between overhead due to transmission of a reference signal andchannel estimation performance.

Furthermore, an embodiment of the present invention provides amultiplexing method for extending the number of ports for transmitting ademodulation reference signal.

Furthermore, an embodiment of the present invention provides a methodfor mapping a reference signal using a code division multiplexing schemeon a frequency axis and a time axis.

Furthermore, an embodiment of the present invention provides amultiplexing and repeating method for extending the number of ports fortransmitting a demodulation reference signal.

Objects of the present invention are not limited to the above-mentionedobjects. That is, other objects that are not mentioned may be obviouslyunderstood by those skilled in the art to which the present inventionpertains from the following description.

Technical Solution

Furthermore, in this specification, a method for performing, userequipment (UE), to decode data in a wireless communication system,includes: receiving a demodulation reference signal (DMRS) configured bya base station according to a specific pattern from the base stationthrough a DMRS symbol, the demodulation reference signal beingtransmitted on a specific antenna port and located on the same one ortwo time-axis symbols as at least one other demodulation referencesignal transmitted on another antenna port, the demodulation referencesignal being mapped to the one or two time-axis symbols using at leastone of a first code division multiplexing (CDM) on a frequency axis or asecond CDM on a time axis, and the specific pattern being determinedaccording to characteristics of a frequency band in which thedemodulation reference signal is transmitted; and decoding the datausing the demodulation reference signal.

The demodulation reference signal is located on the one or two time axissymbols based on at least one of the number of transport layers, a portindex, a rank, or the maximum number of transport ports.

When the demodulation reference signal is located on one time-axissymbol, the demodulation reference signal is mapped using the first CDM.

When the demodulation reference signal is located on two time-axissymbols, the demodulation reference signal is mapped using the secondCDM.

The method further includes: receiving a signal indicating whether toapply the second CDM from the base station, in which the demodulationreference signal is mapped using the first CDM and the second CDM, whenthe signal indicates that the second CDM is applied.

The method further includes: receiving a signal indicating a length ofthe first CDM from the base station when the first CDM is applied, inwhich it is determined whether to apply the second CDM depending on thelength of the first CDM.

When the demodulation reference signal is mapped using the first CDM andthe second CDM, a type of orthogonal cover codes (OCCs) applied to thesecond CDM is limited to at least one type by the base station.

The method further includes: receiving the signal indicating the atleast one type from the base station.

Furthermore, in this specification, user equipment (UE) decoding data ina wireless communication system includes: a radio frequency unitconfigured to transmit and receive a radio signal to and from theoutside; and a processor configured to functionally coupled to the radiofrequency unit, in which the processor receives a demodulation referencesignal (DMRS) configured by a base station according to a specificpattern from the base station through a DMRS symbol, the demodulationreference signal being transmitted on a specific antenna port andlocated on the same one or two time-axis symbols as at least one otherdemodulation reference signal transmitted on another antenna port, thedemodulation reference signal being mapped to the one or two time-axissymbols using at least one of a first code division multiplexing (CDM)on a frequency axis or a second CDM on a time axis, and the specificpattern being determined according to characteristics of a frequencyband in which the demodulation reference signal is transmitted, anddecodes the data using the demodulation reference signal.

Advantageous Effects

According to the present invention, it is possible to decode data byestimating the common phase error (CPE) and carrier frequency offset(CFO) values due to the Doppler effect through the DMRS.

In addition, according to the present invention, it is possible toestimating the channel through additional DMRS in the high Dopplerenvironment.

In addition, according to the present invention, it is possible tochange the pattern of the DMRS according to the situation of the UE bymapping the demodulation reference signal in consideration of thetrade-off between the overhead due to the transmission of the referencesignal and the channel estimation performance.

In addition, according to the present invention, it is possible toextend the number of ports for transmitting the demodulation referencesignal by using the code division multiplexing scheme on the time axisas well as the frequency axis.

In addition, according to the present invention, it is possible toextend the number of ports for transmitting the demodulation referencesignal by mapping the reference signal using the multiplexing andrepetition.

Effects which can be achieved by the present invention are not limitedto the above-mentioned effects. That is, other objects that are notmentioned may be obviously understood by those skilled in the art towhich the present invention pertains from the following description.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included as part of the detaileddescription to assist understanding of the invention, illustrateembodiments of the invention and explain the technical features of theinvention together with the detailed description.

FIG. 1 is a diagram illustrating a structure of a radio frame in awireless communication system to which the present invention can beapplied;

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which the present invention can beapplied;

FIG. 3 is a diagram illustrating a structure of a downlink subframe in awireless communication system to which the present invention can beapplied;

FIG. 4 is a diagram illustrating a structure of an uplink subframe in awireless communication system to which the present invention can beapplied;

FIG. 5 is a diagram illustrating a reference signal pattern mapped to adownlink resource block pair in a wireless communication system to whichthe present invention can be applied;

FIG. 6 is a diagram illustrating an example of a resource area structureused in a communication system using mmWave to which the presentinvention can be applied;

FIGS. 7 and 8 are diagrams illustrating an example of a pattern of ademodulation reference signal proposed herein;

FIGS. 9 to 13 are diagrams illustrating an example of a method formapping DMRSs using a repetition pattern proposed herein;

FIG. 14 is a flowchart illustrating an example of a method forgenerating and transmitting a demodulation reference signal proposedherein;

FIG. 15 is a flowchart illustrating an example of a method for decodingdata by receiving a demodulation reference signal proposed herein; and

FIG. 16 is a diagram illustrating an example of an internal blockdiagram of a wireless device to which the present invention can beapplied.

MODE FOR INVENTION

Some embodiments of the present invention are described in detail withreference to the accompanying drawings. A detailed description to bedisclosed along with the accompanying drawings are intended to describesome embodiments of the present invention and are not intended todescribe a sole embodiment of the present invention. The followingdetailed description includes more details in order to provide fullunderstanding of the present invention. However, those skilled in theart will understand that the present invention may be implementedwithout such more details.

In some cases, in order to avoid that the concept of the presentinvention becomes vague, known structures and devices are omitted or maybe shown in a block diagram form based on the core functions of eachstructure and device.

In this specification, a base station has the meaning of a terminal nodeof a network over which the base station directly communicates with adevice. In this document, a specific operation that is described to beperformed by a base station may be performed by an upper node of thebase station according to circumstances. That is, it is evident that ina network including a plurality of network nodes including a basestation, various operations performed for communication with a devicemay be performed by the base station or other network nodes other thanthe base station. The base station (BS) may be substituted with anotherterm, such as a fixed station, a Node B, an eNB (evolved-NodeB), a BaseTransceiver System (BTS), or an access point (AP). Furthermore, thedevice may be fixed or may have mobility and may be substituted withanother term, such as User Equipment (UE), a Mobile Station (MS), a UserTerminal (UT), a Mobile Subscriber Station (MSS), a Subscriber Station(SS), an Advanced Mobile Station (AMS), a Wireless Terminal (WT), aMachine-Type Communication (MTC) device, a Machine-to-Machine (M2M)device, or a Device-to-Device (D2D) device.

Hereinafter, downlink (DL) means communication from an eNB to UE, anduplink (UL) means communication from UE to an eNB. In DL, a transmittermay be part of an eNB, and a receiver may be part of UE. In UL, atransmitter may be part of UE, and a receiver may be part of an eNB.

Specific terms used in the following description have been provided tohelp understanding of the present invention, and the use of suchspecific terms may be changed in various forms without departing fromthe technical sprit of the present invention.

The following technologies may be used in a variety of wirelesscommunication systems, such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), and Non-OrthogonalMultiple Access (NOMA). CDMA may be implemented using a radiotechnology, such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asGlobal System for Mobile communications (GSM)/General Packet RadioService (GPRS)/Enhanced Data rates for GSM Evolution (EDGE). OFDMA maybe implemented using a radio technology, such as Institute of Electricaland Electronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or Evolved UTRA (E-UTRA). UTRA is part of a UniversalMobile Telecommunications System (UMTS). 3rd Generation PartnershipProject (3GPP) Long Term Evolution (LTE) is part of an Evolved UMTS(E-UMTS) using evolved UMTS Terrestrial Radio Access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-Advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System to which the Present Invention May be Applied

FIG. 1 shows the structure of a radio frame in a wireless communicationsystem to which an embodiment of the present invention may be applied.

3GPP LTE/LTE-A support a radio frame structure type 1 which may beapplicable to Frequency Division Duplex (FDD) and a radio framestructure which may be applicable to Time Division Duplex (TDD).

The size of a radio frame in the time domain is represented as amultiple of a time unit of T_s=1/(15000*2048). A UL and DL transmissionincludes the radio frame having a duration of T_f=307200*T_s=10 ms.

FIG. 1(a) exemplifies a radio frame structure type 1. The type 1 radioframe may be applied to both of full duplex FDD and half duplex FDD.

A radio frame includes 10 subframes. A radio frame includes 20 slots ofT_slot=15360*T_s=0.5 ms length, and 0 to 19 indexes are given to each ofthe slots. One subframe includes consecutive two slots in the timedomain, and subframe i includes slot 2i and slot 2i+1. The time requiredfor transmitting a subframe is referred to as a transmission timeinterval (TTI). For example, the length of the subframe i may be 1 msand the length of a slot may be 0.5 ms.

A UL transmission and a DL transmission I the FDD are distinguished inthe frequency domain. Whereas there is no restriction in the full duplexFDD, a UE may not transmit and receive simultaneously in the half duplexFDD operation.

One slot includes a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols in the time domain and includes a pluralityof Resource Blocks (RBs) in a frequency domain. In 3GPP LTE, OFDMsymbols are used to represent one symbol period because OFDMA is used indownlink. An OFDM symbol may be called one SC-FDMA symbol or symbolperiod. An RB is a resource allocation unit and includes a plurality ofcontiguous subcarriers in one slot.

FIG. 1(b) shows frame structure type 2.

A type 2 radio frame includes two half frame of 153600*T_s=5 ms lengtheach. Each half frame includes 5 subframes of 30720*T_s=1 ms length.

In the frame structure type 2 of a TDD system, an uplink-downlinkconfiguration is a rule indicating whether uplink and downlink areallocated (or reserved) to all subframes.

Table 1 shows the uplink-downlink configuration.

TABLE 1 Downlink- to- Uplink Uplink- Switch- Downlink point Subframenumber configuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U DS U U U 1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  DS U U U D D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D DD D 6 5 ms D S U U U D S U U D

Referring to Table 1, in each subframe of the radio frame, ‘D’represents a subframe for a DL transmission, ‘U’ represents a subframefor UL transmission, and ‘S’ represents a special subframe includingthree types of fields including a Downlink Pilot Time Slot (DwPTS), aGuard Period (GP), and a Uplink Pilot Time Slot (UpPTS).

A DwPTS is used for an initial cell search, synchronization or channelestimation in a UE. A UpPTS is used for channel estimation in an eNB andfor synchronizing a UL transmission synchronization of a UE. A GP isduration for removing interference occurred in a UL owing to multi-pathdelay of a DL signal between a UL and a DL.

Each subframe i includes slot 2i and slot 2i+1 of T_slot=15360*T_s=0.5ms.

The UL-DL configuration may be classified into 7 types, and the positionand/or the number of a DL subframe, a special subframe and a UL subframeare different for each configuration.

A point of time at which a change is performed from downlink to uplinkor a point of time at which a change is performed from uplink todownlink is called a switching point. The periodicity of the switchingpoint means a cycle in which an uplink subframe and a downlink subframeare changed is identically repeated. Both 5 ms and 10 ms are supportedin the periodicity of a switching point. If the periodicity of aswitching point has a cycle of a 5 ms downlink-uplink switching point,the special subframe S is present in each half frame. If the periodicityof a switching point has a cycle of a 5 ms downlink-uplink switchingpoint, the special subframe S is present in the first half-frame only.

In all the configurations, 0 and 5 subframes and a DwPTS are used foronly downlink transmission. An UpPTS and a subframe subsequent to asubframe are always used for uplink transmission.

Such uplink-downlink configurations may be known to both an eNB and UEas system information. An eNB may notify UE of a change of theuplink-downlink allocation state of a radio frame by transmitting onlythe index of uplink-downlink configuration information to the UEwhenever the uplink-downlink configuration information is changed.Furthermore, configuration information is kind of downlink controlinformation and may be transmitted through a Physical Downlink ControlChannel (PDCCH) like other scheduling information. Configurationinformation may be transmitted to all UEs within a cell through abroadcast channel as broadcasting information.

Table 2 represents configuration (length of DwPTS/GP/UpPTS) of a specialsubframe.

TABLE 2 Normal cyclic prefix in downlink UpPTS Extended cyclic prefix indownlink Normal cyclic Extended UpPTS Special subframe prefix cyclicprefix Normal cyclic Extended cyclic configuration DwPTS in uplink inuplink DwPTS prefix in uplink prefix in uplink 0  6592 · T_(s) 2192 ·T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The structure of a radio subframe according to the example of FIG. 1 isjust an example, and the number of subcarriers included in a radioframe, the number of slots included in a subframe and the number of OFDMsymbols included in a slot may be changed in various manners.

FIG. 2 is a diagram illustrating a resource grid for one downlink slotin a wireless communication system to which an embodiment of the presentinvention may be applied.

Referring to FIG. 2, one downlink slot includes a plurality of OFDMsymbols in a time domain. It is described herein that one downlink slotincludes 7 OFDMA symbols and one resource block includes 12 subcarriersfor exemplary purposes only, and the present invention is not limitedthereto.

Each element on the resource grid is referred to as a resource element,and one resource block (RB) includes 12×7 resource elements. The numberof RBs NADL included in a downlink slot depends on a downlinktransmission bandwidth.

The structure of an uplink slot may be the same as that of a downlinkslot.

FIG. 3 shows the structure of a downlink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 3, a maximum of three OFDM symbols located in a frontportion of a first slot of a subframe correspond to a control region inwhich control channels are allocated, and the remaining OFDM symbolscorrespond to a data region in which a physical downlink shared channel(PDSCH) is allocated. Downlink control channels used in 3GPP LTEinclude, for example, a physical control format indicator channel(PCFICH), a physical downlink control channel (PDCCH), and a physicalhybrid-ARQ indicator channel (PHICH).

A PCFICH is transmitted in the first OFDM symbol of a subframe andcarries information about the number of OFDM symbols (i.e., the size ofa control region) which is used to transmit control channels within thesubframe. A PHICH is a response channel for uplink and carries anacknowledgement (ACK)/not-acknowledgement (NACK) signal for a HybridAutomatic Repeat Request (HARD). Control information transmitted in aPDCCH is called Downlink Control Information (DCI). DCI includes uplinkresource allocation information, downlink resource allocationinformation, or an uplink transmission (Tx) power control command for aspecific UE group.

A PDCCH may carry information about the resource allocation andtransport format of a downlink shared channel (DL-SCH) (this is alsocalled an “downlink grant”), resource allocation information about anuplink shared channel (UL-SCH) (this is also called a “uplink grant”),paging information on a PCH, system information on a DL-SCH, theresource allocation of a higher layer control message, such as a randomaccess response transmitted on a PDSCH, a set of transmission powercontrol commands for individual UE within specific UE group, and theactivation of a Voice over Internet Protocol (VoIP), etc. A plurality ofPDCCHs may be transmitted within the control region, and UE may monitora plurality of PDCCHs. A PDCCH is transmitted on a single ControlChannel Element (CCE) or an aggregation of some contiguous CCEs. A CCEis a logical allocation unit that is used to provide a PDCCH with acoding rate according to the state of a radio channel. A CCE correspondsto a plurality of resource element groups. The format of a PDCCH and thenumber of available bits of a PDCCH are determined by an associationrelationship between the number of CCEs and a coding rate provided byCCEs.

An eNB determines the format of a PDCCH based on DCI to be transmittedto UE and attaches a Cyclic Redundancy Check (CRC) to controlinformation. A unique identifier (this is called a Radio NetworkTemporary Identifier (RNTI)) is masked to the CRC depending on the owneror use of a PDCCH. In the case that the PDCCH is a PDCCH for specificUE, an identifier unique to the UE, for example, a Cell-RNTI (C-RNTI)may be masked to the CRC. Or, in the case that the PDCCH is a PDCCH fora paging message, a paging indication identifier, for example, aPaging-RNTI (P-RNTI) may be masked to the CRC. If the PDCCH is a PDCCHfor system information, more specifically, a System Information Block(SIB), a system information identifier, for example, a SystemInformation-RNTI (SI-RNTI) may be masked to the CRC. A RandomAccess-RNTI (RA-RNTI) may be masked to the CRC in order to indicate arandom access response which is a response to the transmission of arandom access preamble by UE.

FIG. 4 shows the structure of an uplink subframe in a wirelesscommunication system to which an embodiment of the present invention maybe applied.

Referring to FIG. 4, the uplink subframe may be divided into a controlregion and a data region in a frequency domain. A physical uplinkcontrol channel (PUCCH) carrying uplink control information is allocatedto the control region. A physical uplink shared channel (PUSCH) carryinguser data is allocated to the data region. In order to maintain singlecarrier characteristic, one UE does not send a PUCCH and a PUSCH at thesame time.

A Resource Block (RB) pair is allocated to a PUCCH for one UE within asubframe. RBs belonging to an RB pair occupy different subcarriers ineach of 2 slots. This is called that an RB pair allocated to a PUCCH isfrequency-hopped in a slot boundary.

Reference Signal (RS)

In a wireless communication system, a signal may be distorted duringtransmission because data is transmitted through a radio channel. Inorder for a terminal to accurately receive a distorted signal, thedistortion of a received signal needs to be corrected using channelinformation. In order to detect channel information, a method ofdetecting channel information using the degree of the distortion of asignal transmission method and a signal known to both the transmissionside and the reception side when they are transmitted through a channelis chiefly used. The aforementioned signal is called a pilot signal orreference signal (RS).

Furthermore recently, when most of mobile communication systems transmita packet, they use a method capable of improving transmission/receptiondata efficiency by adopting multiple transmission antennas and multiplereception antennas instead of using one transmission antenna and onereception antenna used so far. When data is transmitted and receivedusing multiple input/output antennas, a channel state between thetransmission antenna and the reception antenna must be detected in orderto accurately receive the signal. Accordingly, each transmission antennamust have an individual reference signal.

In a mobile communication system, an RS may be basically divided intotwo types depending on its object. There are an RS having an object ofobtaining channel state information and an RS used for datademodulation. The former has an object of obtaining, by a UE, to obtainchannel state information in the downlink. Accordingly, a correspondingRS must be transmitted in a wideband, and a UE must be capable ofreceiving and measuring the RS although the UE does not receive downlinkdata in a specific subframe. Furthermore, the former is also used forradio resources management (RRM) measurement, such as handover. Thelatter is an RS transmitted along with corresponding resources when aneNB transmits the downlink. A UE may perform channel estimation byreceiving a corresponding RS and thus may demodulate data. Thecorresponding RS must be transmitted in a region in which data istransmitted.

A downlink RS includes one common RS (CRS) for the acquisition ofinformation about a channel state shared by all of UEs within a cell andmeasurement, such as handover, and a dedicated RS (DRS) used for datademodulation for only a specific UE. Information for demodulation andchannel measurement can be provided using such RSs. That is, the DRS isused for only data demodulation, and the CRS is used for the two objectsof channel information acquisition and data demodulation.

The reception side (i.e., UE) measures a channel state based on a CRSand feeds an indicator related to channel quality, such as a channelquality indicator (CQI), a precoding matrix index (PMI) and/or a rankindicator (RI), back to the transmission side (i.e., an eNB). The CRS isalso called a cell-specific RS. In contrast, a reference signal relatedto the feedback of channel state information (CSI) may be defined as aCSI-RS.

The DRS may be transmitted through resource elements if data on a PDSCHneeds to be demodulated. A UE may receive information about whether aDRS is present through a higher layer, and the DRS is valid only if acorresponding PDSCH has been mapped. The DRS may also be called aUE-specific RS or demodulation RS (DMRS).

FIG. 5 illustrates reference signal patterns mapped to downlink resourceblock pairs in a wireless communication system to which the presentinvention may be applied.

Referring to FIG. 5, a downlink resource block pair, that is, a unit inwhich a reference signal is mapped, may be represented in the form ofone subframe in a time domain X 12 subcarriers in a frequency domain.That is, in a time axis (an x axis), one resource block pair has alength of 14 OFDM symbols in the case of a normal cyclic prefix (CP)(FIG. 5a ) and has a length of 12 OFDM symbols in the case of anextended cyclic prefix (CP) (FIG. 5b ). In the resource block lattice,resource elements (REs) indicated by “0”, “1”, “2”, and “3” mean thelocations of the CRSs of antenna port indices “0”, “1”, “2”, and “3”,respectively, and REs indicated by “D” mean the location of a DRS.

A CRS is described in more detail below. The CRS is a reference signalwhich is used to estimate the channel of a physical antenna and may bereceived by all UEs located within a cell in common. The CRS isdistributed to a full frequency bandwidth. That is, the CRS iscell-specific signal and is transmitted every subframe in a wideband.Furthermore, the CRS may be used for channel quality information (CSI)and data demodulation.

A CRS is defined in various formats depending on an antenna array on thetransmitting side (eNB). In the 3GPP LTE system (e.g., Release-8), an RSfor a maximum four antenna ports is transmitted depending on the numberof transmission antennas of an eNB. The side from which a downlinksignal is transmitted has three types of antenna arrays, such as asingle transmission antenna, two transmission antennas and fourtransmission antennas. For example, in the case that the number oftransmission antennas of an eNB is two, CRSs for a No. 0 antenna portand a No. 1 antenna port are transmitted. In the case that the number oftransmission antennas of an eNB is four, CRSs for No. 0 to No. 3 antennaports are transmitted.

In the case that an eNB uses a single transmission antenna, referencesignals for a single antenna port are arrayed.

In the case that an eNB uses two transmission antennas, referencesignals for two transmission antenna ports are arrayed using a timedivision multiplexing (TDM) scheme and/or a frequency divisionmultiplexing (FDM) scheme. That is, different time resources and/ordifferent frequency resources are allocated in order to distinguishbetween reference signals for two antenna ports.

Furthermore, in the case that an eNB uses four transmission antennas,reference signals for four transmission antenna ports are arrayed usingthe TDM and/or FDM schemes. Channel information measured by thereception side (i.e., UE) of a downlink signal may be used to demodulatedata transmitted using a transmission scheme, such as singletransmission antenna transmission, transmission diversity, closed-loopspatial multiplexing, open-loop spatial multiplexing or amulti-user-multi-input/output (MIMO) antenna.

In the case that a multi-input multi-output antenna is supported, when aRS is transmitted by a specific antenna port, the RS is transmitted inthe locations of resource elements specified depending on a pattern ofthe RS and is not transmitted in the locations of resource elementsspecified for other antenna ports. That is, RSs between differentantennas do not overlap.

The rule of mapping a CRS to a resource block is defined as below.

$\begin{matrix}{{k = {{6m} + {( {v + v_{shift}} ){mod}\; 6}}}{l = \{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \{ {0,1} \}} \\1 & {{{if}\mspace{14mu} p} \in \{ {2,3} \}}\end{matrix}m} = 0},1,\ldots \mspace{11mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu} {and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu} {and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu} {and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu} {and}\mspace{14mu} l} \neq 0}} \\{3( {n_{s}\mspace{11mu} {mod}\; 2} )} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3( {n_{s}\mspace{11mu} {mod}\; 2} )}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}\mspace{11mu} {mod}\; 6}} }}} }} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

In Equation 1, k and l represent the subcarrier index and the symbolindex, respectively and p represents the antenna port. N_(symb) ^(DL)represents the number of OFDM symbols in one downlink slot and N_(RB)^(DL) represents the number of radio resources allocated to thedownlink, ns represents a slot index and, N_(ID) ^(cell) represents acell ID. The mod represents an modulo operation. The position of thereference signal varies depending on the ν_(shift) value in thefrequency domain. Since ν_(shift) is subordinated to the cell ID, theposition of the reference signal has various frequency shift valuesaccording to the cell.

In more detail, the position of the CRS may be shifted in the frequencydomain according to the cell in order to improve channel estimationperformance through the CRS. For example, when the reference signal ispositioned at an interval of three subcarriers, reference signals in onecell are allocated to a 3k-th subcarrier and a reference signal inanother cell is allocated to a 3k+1-th subcarrier. In terms of oneantenna port, the reference signals are arrayed at an interval of sixresource elements in the frequency domain and separated from a referencesignal allocated to another antenna port at an interval of threeresource elements.

In the time domain, the reference signals are arrayed at a constantinterval from symbol index 0 of each slot. The time interval is defineddifferently according to a cyclic shift length. In the case of thenormal cyclic shift, the reference signal is positioned at symbolindexes 0 and 4 of the slot and in the case of the extended CP, thereference signal is positioned at symbol indexes 0 and 3 of the slot. Areference signal for an antenna port having a maximum value between twoantenna ports is defined in one OFDM symbol. Therefore, in the case oftransmission of four transmitting antennas, reference signals forreference signal antenna ports 0 and 1 are positioned at symbol indexes0 and 4 (symbol indexes 0 and 3 in the case of the extended CP) andreference signals for antenna ports 2 and 3 are positioned at symbolindex 1 of the slot. The positions of the reference signals for antennaports 2 and 3 in the frequency domain are exchanged with each other in asecond slot.

Hereinafter, when the DRS is described in more detail, the DRS is usedfor demodulating data. A precoding weight used for a specific UE in theMIMO antenna transmission is used without a change in order to estimatea channel associated with and corresponding to a transmission channeltransmitted in each transmitting antenna when the terminal receives thereference signal.

The 3 GPP LTE system (for example, release-8) supports a maximum of fourtransmitting antennas and a DRS for rank 1 beamforming is defined. TheDRS for the rank 1 beamforming also means a reference signal for antennaport index 5.

A rule of mapping the DRS to the resource block is defined as below.Equation 2 shows the case of the normal CP and Equation 3 shows the caseof the extended CP.

$\begin{matrix}{{k = {{( k^{\prime} ){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \{ {2,3} \}} \\{{4m^{\prime}} + {( {2 + v_{shift}} )\; {mod}\; 4}} & {{{if}\mspace{14mu} l} \in \{ {5,6} \}}\end{matrix}l} = \{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} - 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}\mspace{14mu} {mod}\; 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}\mspace{14mu} {mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots \mspace{11mu},{{{3N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}\; {mod}\; 3}}} } } }} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack \\{{k = {{( k^{\prime} ){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {( {2 + v_{shift}} )\; {mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \{ {{\begin{matrix}4 & {l^{\prime} \in \{ {0,2} \}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}\mspace{14mu} {mod}\; 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}\mspace{14mu} {mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots \mspace{11mu},{{{4N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}\; {mod}\; 3}}} } } }} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

In Equations 3 and 4, k and 1 represent the subcarrier index and thesymbol index, respectively and p represents the antenna port. N_(sc)^(RB) represents the size of the resource block in the frequency domainand is expressed as the number of subcarriers. n_(PRB) represents thenumber of physical resource blocks. N_(RB) ^(PDSCH) represents afrequency band of the resource block for the PDSCH transmission. nsrepresents the slot index and N_(ID) ^(cell) represents the cell ID. Themod represents the modulo operation. The position of the referencesignal varies depending on the value in the frequency domain. Sinceν_(shift) is subordinated to the cell ID, the position of the referencesignal has various frequency shift values according to the cell.

In an LTE-A system of an evolved form of the LTE system, the designneeds to be performed to support a maximum of 8 transmission antennas inthe downlink of a base station. Accordingly, an RS for the maximum of 8transmission antennas must be also supported. In the LTE system, only adownlink RS for a maximum of 4 antenna ports has been defined. In thecase that a base station has 4 or a maximum of 8 downlink transmissionantennas in the LTE-A system, an RS for such antenna ports needs to beadditionally defined and designed. Regarding the RS for a maximum of 8transmission antenna ports, both the above-described RS for channelmeasurement and the above-described RS for data demodulation must bedesigned.

One of important considerations in designing an LTE-A system is backwardcompatibility. That is, an LTE user equipment must well operate in theLTE-A system without any difficulty, and the system must support this.From a viewpoint of RS transmission, an RS for a maximum of 8transmission antenna ports must be additionally defined in thetime-frequency domain in which a CRS defined in LTE is transmitted everysubframe in a full band. In the LTE-A system, if an RS pattern for themaximum of 8 transmission antenna is added to a full band every subframeusing a method, such as that for the CRS of the existing LTE, RSoverhead excessively increases.

Accordingly, an RS newly designed in the LTE-A system may be basicallydivided into two types, that is, an RS for channel measurement for theselection of an MCS, PMI, and the like (channel state information-RS,channel state indication-RS (CSI-RS), etc.) and a data demodulation(DM)-RS for data demodulation transmitted in 8 transmission antennas.

The existing CRS is used for channel measurement, the measurement ofhandover, etc. and for data demodulation, whereas the CSI-RS for channelmeasurement is designed for a channel measurement-oriented purpose.Furthermore, the CSI-RS for channel measurement may also be used for themeasurement of handover. Since the CSI-RS is used to obtain informationon the channel state only, it does not need to be transmitted everysubframe unlike the CRS. In order to reduce overhead of the CSI-RS, theCSI-RS is intermittently transmitted on the time axis.

A DM-RS is dedicatedly transmitted to a UE scheduled in a correspondingtime-frequency domain for data demodulation. That is, the DM-RS of aspecific UE is transmitted only in a region in which a corresponding UEis scheduled, that is, only in a time-frequency domain in which data isreceived.

In the LTE-A system, an eNB has to transmit a CSI-RS for all antennaports. To transmit a CSI-RS for a maximum of 8 transmission antennaports every subframe has a disadvantage in that overhead is too great.Accordingly, the CSI-RS is not transmitted every subframe, but needs tobe intermittently transmitted in the time axis in order to reducecorresponding overhead. That is, the CSI-RS may be periodicallytransmitted in the period of a multiple of one subframe or may betransmitted in a specific transmission pattern. In this case, the periodor pattern in which the CSI-RS is transmitted may be configured by theeNB.

In order to measure a CSI-RS, a UE must be aware of the transmissionsubframe index of a CSI-RS for each CSI-RS antenna port of a cell towhich the UE belongs, a CSI-RS resource element (RE) time-frequencyposition within the transmission subframe, and information on a CSI-RSsequence.

In the LTE-A system, an eNB needs to transmit a CSI-RS with respect toeach of a maximum of 8 antenna ports. Resources used for the CSI-RStransmission of different antenna ports need to be orthogonal. When oneeNB transmits CSI-RSs for different antenna ports, it may orthogonallyallocate resources according to the FDM/TDM scheme by mapping theCSI-RSs for the respective antenna ports to different REs.Alternatively, the eNB may transmit the CSI-RSs for different antennaports according to a CDM scheme for mapping the CSI-RSs to orthogonalcodes.

When an eNB notifies its own cell UE of information on a CSI-RS, first,it has to notify the UE of information on a time-frequency to which aCSI-RS for each antenna port is mapped. Specifically, the informationincludes subframe numbers in which a CSI-RS is transmitted or the periodin which a CSI-RS is transmitted, a subframe offset in which a CSI-RS istransmitted, an OFDM symbol number in which a CSI-RS RE of a specificantenna is transmitted, frequency spacing, an offset or shift value ofan RE in the frequency axis, and so on.

Communication System Using Ultra High Frequency Band

In a long term evolution (LTE)/LTE advanced (LTE-A) system, error valuesof an oscillator between the UE and the base station are defined asrequirement, and are described as follows.

-   -   UE side frequency error (in TS 36.101)

The UE modulated carrier frequency shall be accurate to within ±0.1 PPMobserved over a period of one time slot (0.5 ms) compared to the carrierfrequency received from the E-UTRA Node B

-   -   eNB side frequency error (in TS 36.104)

Frequency error is the measure of the difference between the actual BStransmit frequency and the assigned frequency.

Meanwhile, the accuracy of the oscillator according to the type of basestations is shown in the following Table 3.

TABLE 3 BS class Accuracy Wide Area BS ±0.05 ppm Local Area BS  ±0.1 ppmHome BS ±0.25 ppm

Therefore, a maximum difference of the oscillator between the basestation and the UE is ±0.1 ppm, and when an error occurs in onedirection, a maximum offset value of 0.2 ppm may occur. This offsetvalue is multiplied by a center frequency and converted into Hz unitsfor each center frequency.

On the other hand, in the OFDM system, the CFO value appears differentlyaccording to a frequency tone subspacing, and in general, even the largeCFO value has a relatively small effect on the OFDM system having asufficiently large frequency tone sub spacing. Therefore, the actual CFOvalue (absolute value) needs to be represented by a relative valueaffecting the OFDM system, which is called a normalized CFO. Thenormalized CFO is represented by a value obtained by dividing the CFOvalue by the frequency tone subspacing. The following Table 4 shows theCFO and the normalized CFO for each center frequency and the errorvalues of the oscillator.

TABLE 4 Center frequency Oscillator Offset (subcarrier spacing) ±0.05ppm ±0.1 ppm ±10 ppm ±20 ppm 2 GHz (15 kHz) ±100 Hz (±0.0067) ±200 Hz(±0.0133) ±20 kHz (±1.3) ±40 kHz (±2.7) 30 GHz (104.25 kHz) ±1.5 kHz(±0.014) ±3 kHz (±0.029) ±300 kHz (±2.9) ±600 kHz (±5.8) 60 GHz (104.25kHz) ±3 kHz (±0.029) ±6 kHz (±0.058) ±600 kHz (±5.8) ±1.2 MHz (±11.5)

In Table 4, when the center frequency is 2 GHz (for example, LTERel-8/9/10), the frequency tone subspacing is assumed to be (15 kHz),and when the center frequency is 30 GHz and 60 GHz, the frequency tonesubspacing is 104.25 kHz, thereby preventing the performancedeterioration considering the Doppler effect for each center frequency.Table 2 above is a mere example, and it is obvious that differentfrequency tone subspacings may be used for the center frequency.

On the other hand, in a situation where the UE moves at a high speed orin a high frequency band, a Doppler spread phenomenon greatly occurs.The Doppler spread causes dispersion in the frequency domain, resultingin the distortion of the received signal from the viewpoint of thereceiver. The Doppler variance can be represented byf_(doppler)=(ν/λ)cos θ. In this case, ν represents a moving speed of theUE, and λ represents a wavelength of the center frequency of the radiowave transmitted. θ represents an angle between the received radio waveand the moving direction of the UE. The following description is basedon the assumption that θ is zero.

In this case, the coherence time is in inverse proportion to the Dopplerspread. If the coherence time is defined as a time interval in which thecorrelation value

onse in the time domain is 50% or more, the coherence time isrepresented by

$T_{c} \approx {\frac{9}{16\; \pi \; f_{doppler}}.}$

In the wireless communication system, the following Equation 4 whichrepresents a geometric mean between the equation for the Doppler spreadand the equation for the coherence time is mainly used.

$\begin{matrix}{T_{c} = {\sqrt{\frac{9}{16\; \pi \; f_{doppler}}} = \frac{0.423}{f_{doppler}}}} & \lbrack {{Equation}\mspace{14mu} 4} \rbrack\end{matrix}$

FIG. 6 illustrates an example of a resource area structure used in acommunication system using mmWave to which the present invention can beapplied.

The communication system using the ultra high frequency band such asmmWave uses a frequency band different in physical properties from theconventional LTE/LTE-A communication system. Accordingly, in thecommunication system using the ultra high frequency band, a resourcestructure having a form different from that of the resource region usedin the conventional communication system is being discussed. FIG. 6shows an example of a downlink resource structure of a new communicationsystem.

Considering a resource block pair (RB pair) including 14 orthogonalfrequency division multiplexing (OFDM) symbols on a horizontal axis and12 frequency tones on a vertical axis, first two (or three) OFDM symbols1310 may be allocated to a control channel (for example, a physicaldownlink control channel (PDCCH)), the next one to two OFDM symbols 620may be allocated a DeModulation reference signal (DMRS), and theremaining OFDM symbols may be allocated a data channel (for example,physical downlink shared channel (PDSCH)).

Meanwhile, in the resource region structure as shown in FIG. 6, PCRS orPNRS or PTRS for the CPE (or CFO) estimation described above may becarried on a part of a resource element (RE) of the region 630 to whichthe data channel is allocated and transmitted to the UE. Such a signalis a signal for estimating phase noise, and may be a pilot signal asdescribed above or a signal whose data signal is changed or duplicated.

The present invention proposes a method of transmitting DMRS for channelestimation in downlink or uplink.

FIGS. 7 and 8 are diagrams illustrating an example of a pattern of ademodulation reference signal proposed herein.

Reference to FIGS. 7 and 8, a demodulation reference signal forestimating a channel may be mapped to one symbol or two symbolsaccording to the maximum number of antenna ports.

In detail, the uplink DMRS and the downlink DMRS may be generated andmapped to the resource region by the following method. FIG. 7illustrates an example of an uplink or downlink DMRS mapped to aphysical resource according to type 1, and FIG. 8 illustrates an exampleof an uplink or downlink DMRS mapped to a physical resource according totype 2.

Demodulation Reference Signal for PUSCH

A reference signal sequence r(m) for generating the downlink DMRS isgenerated by the following Equation 5 when transform precoding for PUSCHis not allowed.

In this case, an example of the case where the transform precoding forthe PUSCH is not allowed may be a case of generating a transmissionsignal of a CP-OFDM scheme

$\begin{matrix}{{r(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}} & \lbrack {{Equation}\mspace{14mu} 5} \rbrack\end{matrix}$

Here, c(i) means a pseudo-random sequence.

If the transform precoding for the PUSCH is allowed, the referencesignal sequence r(m) is generated by the following Equation 6.

In this case, an example of the case where the transform precoding forthe PUSCH is allowed may be a case of generating a transmission signalof a DFT-S-OFDM scheme.

$\begin{matrix}{{r(m)} = e^{{- j}\frac{\pi \; {{qm}{({m + 1})}}}{L}}} & \lbrack {{Equation}\mspace{14mu} 6} \rbrack\end{matrix}$

The DMRS of the PUSCH generated is mapped to a physical resourceaccording to type 1 or type 2 given by higher layer parameters asillustrated in FIGS. 8 and 9.

In this case, the DMRS may be mapped to a single symbol or a doublesymbol according to the number of antenna ports.

If the transform precoding is not allowed, the reference signal sequencer(m) may be mapped to the physical resource by the following Equation 7.

$\begin{matrix}{{a_{k,l}^{({p,\mu})} = {\beta_{DMRS}{{w_{f}( k^{\prime} )} \cdot {w_{t}( l^{\prime} )} \cdot {r( {{2m} + k^{\prime} + m_{0}} )}}}}{k = \{ {{{\begin{matrix}{k_{0} + {4m} + {2k^{\prime}} + \Delta} & {{Configuration}\mspace{14mu} {type}\mspace{11mu} 1} \\{k_{0} + {6m} + k^{\prime} + \Delta} & {{Configuration}\mspace{14mu} {type}\mspace{11mu} 2}\end{matrix}k^{\prime}} = 0},{{1l} = {\overset{\_}{l} + l^{\prime}}}} }} & \lbrack {{Equation}\mspace{14mu} 7} \rbrack\end{matrix}$

In the above Equation 7, 1 is defined relative to the start of the PUSCHtransmission, and w_(f)(k′), w_(t)(l′), and Δ are given by the followingTables 5 and 6.

The following Table 5 shows an example of parameters for the DMRS of thePUSCH for type 1.

TABLE 5 w_(f) (k′) w_(t) (l′) p Δ k′ = 0 k′ = 1 l′ = 0 l′ = 1 1000 0 +1+1 +1 +1 1001 0 +1 −1 +1 +1 1002 1 +1 +1 +1 +1 1003 1 +1 −1 +1 +1 1004 0+1 +1 +1 −1 1005 0 +1 −1 +1 −1 1006 1 +1 +1 +1 −1 1007 1 +1 −1 +1 −1

The following Table 6 below shows an example of parameters for the DMRSof the PUSCH for type 2.

TABLE 6 w_(f) (k′) w_(t) (l′) p Δ k′ = 0 k′ = 1 l′ = 0 l′ = 1 1000 0 +1+1 +1 +1 1001 0 +1 −1 +1 +1 1002 2 +1 +1 +1 +1 1003 2 +1 −1 +1 +1 1004 4+1 +1 +1 +1 1005 4 +1 −1 +1 +1 1006 0 +1 +1 +1 −1 1007 0 +1 −1 +1 −11008 2 +1 +1 +1 −1 1009 2 +1 −1 +1 −1 1010 4 +1 +1 +1 −1 1011 4 +1 −1 +1−1

The following Table 7 shows an example of a time domain index l′ and asupported antenna port p according to a higher layer parameterUL_DMRS_dur.

TABLE 7 p UL_DMRS_dur l′ Type 1 Type 2 Single-symbol DMRS 0 1000-10031000-1005 Double-symbol DMRS 0, 1 1000-1007 1000-1011

The following Table 8 shows an example of a start position l of the DMRSof the PUSCH.

TABLE 8 l Single symbol DMRS Double symbol DMRS Uplink PUSCH PUSCH PUSCHPUSCH DMRS mapping mapping mapping mapping parameter type A type B typeA type B 0 l₀ l₀ l₀ l₀ 1 l₀, 7 2 l₀, 9 3 l₀, 11

Demodulation Reference Signals for PDSCH

The reference signal sequence r(m) for generating the downlink DMRS isgenerated by the following Equation 8.

$\begin{matrix}{{r(m)} = {{\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {2m} )}}} )} + {j\frac{1}{\sqrt{2}}( {1 - {2 \cdot {c( {{2m} + 1} )}}} )}}} & \lbrack {{Equation}\mspace{14mu} 8} \rbrack\end{matrix}$

Here, c(i) means a pseudo-random sequence.

The DMRS of the PDSCH generated is mapped to a physical resourceaccording to type 1 or type 2 given by higher layer parameters asillustrated in FIGS. 8 and 9.

In this case, the reference signal sequence r(m) may be mapped to aphysical resource by the following Equation 9.

$\begin{matrix}{{a_{k,l}^{({p,\mu})} = {\beta_{DMRS}{{w_{f}( k^{\prime} )} \cdot {w_{t}( l^{\prime} )} \cdot {r( {{2m} + k^{\prime} + m_{0}} )}}}}{k = \{ {{{\begin{matrix}{k_{0} + {4m} + {2k^{\prime}} + \Delta} & {{Configuration}\mspace{14mu} {type}\mspace{11mu} 1} \\{k_{0} + {6m} + k^{\prime} + \Delta} & {{Configuration}\mspace{14mu} {type}\mspace{11mu} 2}\end{matrix}k^{\prime}} = 0},{{1l} = {\overset{\_}{l} + l^{\prime}}}} }} & \lbrack {{Equation}\mspace{14mu} 9} \rbrack\end{matrix}$

In the above Equation 9, 1 is defined relative to the start of the slot,and w_(f)(k′), w_(t)(l′), and Δ are given by the following Tables 11 and12.

The time axis index l′ and the supported antenna ports p vary dependingon the higher layer parameter DL_DMRS_dur according to the followingTable 12. The l value varies depends on a higher layer parameterDL_DMRS_add_pos given in Table 13, according to the mapping type:

-   -   For PDSCH mapping type A: if the higher layer parameter        DL_DMRS_typeA_pos is equal to 3, then I0=3 and otherwise I0=2.

For PDSCH mapping type B: I0 is mapped to the first OFDM symbol in thePDSCH resource for which the DMRS is scheduled.

The following Table 9 shows an example of parameters for the DMRSconfiguration type 1 of the PDSCH.

TABLE 9 w_(f) (k′) w_(t) (l′) p Δ k′ = 0 k′ = 1 l′ = 0 l′ = 1 1000 0 +1+1 +1 +1 1001 0 +1 −1 +1 +1 1002 1 +1 +1 +1 +1 1003 1 +1 −1 +1 +1 1004 0+1 +1 +1 −1 1005 0 +1 −1 +1 −1 1006 1 +1 +1 +1 −1 1007 1 +1 −1 +1 −1

The following Table 10 shows an example of parameters for the DMRSconfiguration type 2 of the PDSCH.

TABLE 10 w_(f) (k′) w_(t) (l′) p Δ k′ = 0 k′ = 1 l′ = 0 l′ = 1 1000 0 +1+1 +1 +1 1001 0 +1 −1 +1 +1 1002 2 +1 +1 +1 +1 1003 2 +1 −1 +1 +1 1004 4+1 +1 +1 +1 1005 4 +1 −1 +1 +1 1006 0 +1 +1 +1 −1 1007 0 +1 −1 +1 −11008 2 +1 +1 +1 −1 1009 2 +1 −1 +1 −1 1010 4 +1 +1 +1 −1 1011 4 +1 −1 +1−1

The following Table 11 shows an example of l′ which is a duration ofPDSCH DMRS.

TABLE 11 p DL_DMRS_dur l′ Type 1 Type 2 Single-symbol DMRS 0 1000-10031000-1005 Double-symbol DMRS 0, 1 1000-1007 1000-1011

The following Table 12 shows an example of a start position l of theDMRS of the PUSCH.

TABLE 12 l Single symbol DMRS Double symbol DMRS Downlink PDSCH PDSCHPDSCH PDSCH DMRS mapping mapping mapping mapping Parameter type A type Btype A type B 0 l₀ l₀ l₀ l₀ 1 l₀, 7 2 l₀, 9 3 l₀, 11

In the NR system, as described above, the DMRS is defined in units ofOFDM symbols. In order to support the fast decoding speed, the DMRS isplaced in the front symbol of the slot.

The DMRS located at the front symbol of the slot may be called afront-loaded DMRS.

In the present invention, the DMRS located in the front symbol of theslot is called a first DMRS or a front-loaded DMRS for fast decoding.However, in the case of the high Doppler environment, since a channelvariation is large within one slot (or subframe), it is difficult toappropriately compensate for the channel using only the DMRS set in thefront symbol.

Accordingly, in order to solve this problem, additional DMRS can be set.In the present invention, the DMRS is referred to as second DMRS oradditional DMRS.

FIGS. 9 to 13 are diagrams illustrating an example of a method formapping DMRSs using a repetition pattern proposed herein.

Referring to FIGS. 9 to 13, when the number of antenna ports used fortransmitting the DMRS is a predetermined number or more, the basestation may repeat the same mapping pattern to map the DMRS to aresource.

FIGS. 9 and 10 illustrate examples of DMRS mapping patterns forsupporting up to 8 DMRS ports. FIGS. 9A to 9C illustrate examples of amapping pattern for mapping DMRSs using one OFDM symbol, and FIGS. 10Ato 10C illustrate examples of a mapping pattern for mapping DMRSs usingtwo OFDM symbols.

Specifically, FIGS. 9A to 9B show an example of supporting eight DMRSports using the CDM in the frequency domain corresponding to length 4and FDM using two different resources.

On the other hand, FIG. 9C shows an example of supporting eight DMRSports using the CDM in the frequency domain corresponding to length 2and FDM using four different resources.

FIG. 10A shows an example of supporting eight DMRS ports using the CDMin the time domain corresponding to length 2 and FDM using fourdifferent resources. On the other hand, FIG. 10B shows an example ofsupporting eight DMRS ports using the CDM in the frequency domaincorresponding to length 2 and FDM and TDM using two different resources.

FIG. 10C shows an example of mapping DMRSs using a repetition patternrepeating the same pattern.

In FIG. 10C, the DMRS mapping pattern includes two OFDM symbols, but theactual eight DMRS ports are configured within one OFDM symbol and formedof a repetitive structure using the configuration.

Specifically, eight DMRS ports may be supported by the CDM in thefrequency domain corresponding to length 4 and the FDM using twodifferent resources.

Hereinafter, FIG. 9A is called pattern 5, FIG. 9B is called pattern 6,FIG. 9C is called pattern 7, FIG. 10A is called pattern 8, FIG. 10B iscalled pattern 9, and FIG. 10C is called pattern 10.

FIG. 11 is a diagram illustrating an example of spectral efficiencyperformance for each mapping pattern of FIGS. 9 and 10.

As illustrated in FIG. 11, it can be confirmed that in the case ofsupporting eight DMRS ports, better SE performance is obtained comparedto the mapping pattern including one OFDM symbol in pattern 8 andpattern 10 constituting the mapping pattern using two OFDM symbols.

In this case, in the case of pattern 9 using two OFDM symbols, it can beconfirmed that performance deteriorates similarly to a pattern includingone OFDM symbol.

This can be inferred that since pattern 9 uses TDM, the energy of thereference signal is smaller than that of other patterns using two OFDMsymbols.

That is, in the case of the pattern 8 and the pattern 10, since theDMRSs are mapped by using two OFDM symbols for eight ports, the RSenergy can be increased, so it is advantageous in the channelcoefficient estimation.

In addition, the inter-layer interference is reduced due to the gain ofthe channel coefficient estimation, and as a result, the performance maybe improved in terms of the SE even if the RS overhead is increased.

At this time, among the pattern 8 and the pattern 10 using two OFDMsymbols, the pattern 10 may be a mapping pattern that is more suitablefor a high carrier frequency (mmWave) band with a large influence ofphase noise.

Specifically, in the case of the pattern 8, the CDM in the time domainis used. However, when a phase difference occurs between neighboringOFDM symbols due to the influence of the phase noise, performance maydeteriorate in the case of the pattern using the CDM in the time domainthat assumes the same channel between neighboring OFDM symbols asillustrated in the pattern 8.

On the other hand, sine the pattern 10 has a repetitive structure usingthe same pattern between the neighboring OFDM symbols, the error due tothe phase noise can be estimated and compensated. In detail, byestimating a phase difference between neighboring OFDM symbols, andestimating a channel by compensating for the estimated phase difference,an error that may cause deterioration in channel estimation performancemay be compensated in advance.

Therefore, when the number of antenna ports for transmitting the DMRSexceeds a certain number, the DMRS may be mapped to resources using therepetition pattern.

Specifically, when the number of antenna ports for DMRS transmission ismore than a certain number, the base station may increase the CDM lengthin the frequency domain and repeatedly use the same pattern in the timedomain.

In another embodiment of the present invention, the mapping pattern ofthe DMRS may be determined according to the transmission frequency.

In detail, in the high frequency band, the deterioration in the CDMperformance may occur in the time domain due to the influence of phasenoise. Therefore, the a repetition pattern that can estimate andcompensate for the CPE due to the phase noise in the high frequencyband, and provide the sufficient RS energy to prioritize the repetitionpattern capable of improving the channel estimation performance.

For example, if the maximum number of antenna ports is 12, the DMRS maybe mapped as illustrated in FIG. 12.

That is, a mapping pattern configured to support up to 12 DMRS ports inone OFDM symbol may be defined to be repeated in the neighboring OFDMsymbols.

In the above example, the CDM length in the frequency domain increasesto support a plurality of DMRS ports in one OFDM symbol. In the case ofa channel having a long delay spread, the channel estimation performancemay deteriorate due to a channel having high frequency selectivity.

However, in the case of the high frequency band, propagationcharacteristics such as large path attenuation, strong straightness, andsmall transmittance are not good. In addition, with the use of thebeamforming technology to compensate for large path attenuation,channels in the high frequency band have a reduced delay spread.Accordingly, the DMRS pattern having the repetition structure may bereferred to as the mapping pattern suitable for the high frequency band.

Therefore, the transmission frequency band and the DMRS pattern whichmay be preferred in the corresponding frequency band may be determinedby being tied to improve the channel estimation performance according tothe frequency band.

According to another embodiment of the present invention, it may bedetermined whether to apply the CDM in the time domain according to theCDM length in the frequency domain or it is possible to limit the typeof OCC code applied to the CDM in the time domain.

For example, FIG. 10A illustrates an example of supporting eight DMRSports using the CDM in the time domain corresponding to length 2 and theFDM using four different resources. On the other hand, to support thesame eight DMRS ports, as illustrated in FIG. 10C, the repetitionpattern including the CDM in the frequency domain corresponding tolength 4 and the FDM using two different resources may be used.

In the case of the high frequency domain, the CDM in the time domaincauses the deterioration in the channel estimation performance due tothe effect of phase noise. Accordingly, in the case of the highfrequency domain, the effect of the phase noise may be estimated usingthe pattern having the long CDM length and repeating the same among thetwo mapping patterns supporting the eight DMRS ports described above,that is, the pattern illustrated in FIG. 10C, and may be compensated atthe time of the channel estimation.

As in the above example, the application of the CDM in the time domainor the DMRS mapping pattern may vary according to the CDM length in thefrequency domain. As such, the base station may set, in the UE, the DMRSmapping pattern and whether to apply the CDM in the time domain based onthe CDM length in the frequency domain.

When the DMRS is mapped using the repetition pattern, whether to repeatthe pattern may be represented by the CDM on/off in the time domain orby a limitation of an OCC code applied to the CDM.

For example, as illustrated in FIG. 13A, when the CDM of length 3 isapplied in the frequency domain and the CDM of length 2 is applied inthe time domain, an OCC code of length 2 used in the time domain may beequal to [+1, +1], [+1, −1].

In this case, the number of ports multiplexed in the DMRS pattern may be12 ports in total, but when only one OCC code in the time domain isused, multiplexing of a total of 6 ports is possible.

In this case, when the limitation is made to use only OCC codes [+1,+1], the same effect as using the repeating pattern may be obtained.

That is, as illustrated in FIG. 13A, when the CDM length in thefrequency domain is 3, a total of 12 ports may be multiplexed using anOCC code having length 2 in the time domain.

At this time, when the CDM length in the frequency domain is 4 or moreas illustrated in FIGS. 13B and 13C, the same effect as using therepetition pattern may be generated by turning off the CDM in the timedomain or limiting the type of OCC codes to one.

In this case, the base station may explicitly inform the UE of thelimitation on whether to apply the CDM in the time domain or the type ofOCC codes applied to the CDM through at least one of higher layersignaling (for example, RRC, MAC CE, and the like) or DCI.

Alternatively, the base station may inform the CDM length in thefrequency domain through at least one of the higher layer signaling orthe DCI, and the UE may recognize whether to apply the CDM in the timedomain or the limitation of the OCC code applied to the CDM based on theCDM length transmitted from the base station.

In another embodiment of the present invention, the base station mayinform the UE of the CDM on/off in the time domain or the type of OCCcodes applied to the CDM in the time domain through the higher layersignaling or the DCI.

For example, the base station can directly inform the UE of the OCClength in the time domain through a phy layer or the DC.

In this case, if there is no limitation on the OCC code in the timedomain, a total of 12 ports should be supported, but if there is alimitation, only a total of 6 ports will be supported, thereby reducingthe amount of information to be displayed.

When the UE informs such information through the DCI, the UE mayrecognize whether the OCC code of the DMRS pattern is limited, so the UEmay estimate the CPE and the CFO and then receive the DMRS thatcompensates for the estimated value.

When the base station does not explicitly inform the UE of the CDMon/off in the time domain or the type of OCC codes applied to the CDM inthe time domain, it may be assumed that the UE is not MU-paired withother UEs having other OCC codes in the time domain based on atransmission frequency, whether to transmit the PTRS for estimating thephase error due to the phase noise, MCS, or the number of layers.

When the UE satisfies the proposed assumption, the UE may perform areception operation of compensating for a phase difference between DMRSsymbols due to CPEs appearing in each DMRS and then performing combiningof concatenated DMRS symbols.

-   -   □ For example, when the UE uses a transmission frequency of        mmWave band and the MCS uses 256QAM, a process of compensating        for the phase difference between the concatenated DMRS symbols        and then combining the concatenated DMRSs may be performed.□

Even if there is no explicit signaling as in the example of theproposal, the base station may schedule to use only the same OCC code inthe time domain by using other information transmitted to the UE.

In this case, the DMRS can be received under the assumption that the UEis not MU-pared in the specific environment, thereby preventing thedeterioration due to the phase noise and performing the channelestimation.

FIG. 14 is a flowchart illustrating an example of a method forgenerating and transmitting a demodulation reference signal proposedherein.

Referring to FIG. 14, the base station generates a reference signalsequence based on a pseudo random sequence (S14010). In this case, thedemodulation reference signal may be the front-loaded DMRS describedabove.

Thereafter, the base station maps the generated reference signalsequence to one or two time-axis symbols according to a specific pattern(S14020). In this case, the base station may map the reference signalsequence generated according to the specific pattern to one or twotime-axis symbols, and the specific pattern may be one of the patternsdescribed with reference to FIGS. 7 to 13.

The specific pattern may be determined according to the characteristicsof the frequency band in which the demodulation reference signal istransmitted.

As described with reference to FIGS. 7 to 13, the demodulation referencesignal may be multiplexed and mapped to one or two time-axis symbolsthrough the CDM on a frequency axis and/or a time axis.

At this time, the CDM applied on the time axis is called a first CDM,and the CDM applied on the frequency axis is called a second CDM.

Thereafter, the base station generates the demodulation reference signalbased on the mapping of one or two time-axis symbols, and transmits thegenerated demodulation reference signal to the UE using differentantenna ports (S14030 and S14040).

In this case, the demodulation reference signal sequence is mapped onthe same time-axis symbol and transmitted on each specific antenna port,and the demodulation reference signal may be located on the sametime-axis symbol as at least one other demodulation reference signaltransmitted on another antenna port.

FIG. 15 is a flowchart illustrating an example of a method for decodingdata by receiving a demodulation reference signal proposed herein.

Referring to FIG. 15, UE receives a demodulation reference signal (DMRS)configured by a base station according to a specific pattern from a basestation through a DMRS symbol (S15010).

The demodulation reference signal is transmitted on a specific antennaport and may be located on the same one or two time-axis symbols as atleast one other demodulation reference signal transmitted on anotherantenna port.

In addition, as described with reference to FIGS. 7 to 13, thedemodulation reference signal may be multiplexed and mapped to one ortwo time-axis symbols through the CDM on the frequency axis and/or thetime axis.

At this time, the CDM applied on the time axis is called a first CDM,and the CDM applied on the frequency axis is called a second CDM.

The specific pattern may be one of the patterns described with referenceto FIGS. 7 to 13, and may be determined according to characteristics ofthe frequency band in which the demodulation reference signal istransmitted.

Thereafter, the UE may decode data using the received demodulationreference signal (S15020).

FIG. 16 is a diagram illustrating an example of an internal blockdiagram of a wireless device to which the present invention can beapplied.

Here, the wireless device may be a base station and UE, and the basestation includes both a macro base station and a small base station.

As illustrated in FIG. 16, a base station 1610 and UE 1620 include acommunication unit (transmitter and receiver 1613 and RF unit 1623),processors 1611 and 1621, and memories 1612 and 1622.

In addition, the base station and the UE may further include an inputunit and an output unit.

The communication units 1613 and 1623, the processors 1611 and 1621, theinput unit, the output unit, and the memories 1612 and 1622 arefunctionally connected to perform the method proposed herein.

When the communication unit (transmitter and receiver 1613 and RF unit1623) receives information generated from a physical layer protocol (PHYprotocol), the received information is transferred to radio-frequencyspectrum (RF spectrum), filtered, and amplified and the like and thentransmitted to an antenna. In addition, the communication unit functionsto transfer a radio frequency signal (RF signal) received from theantenna to a band that can be processed by the PHY protocol and performfiltering.

The communication unit may also include a switch function for switchingthe transmission and reception functions.

The processors 1611 and 1621 implements functions, processes, and/ormethods proposed herein. The layers of the radio interface protocol maybe implemented by the processor.

The processors may be implemented by a control part, a controller, acontrol unit, a computer, or the like.

The memories 1612 and 1622 are connected to the processor and storeprotocols or parameters for performing an uplink resource allocationmethod.

The processors 1611 and 1612 may include an application-specificintegrated circuit (ASIC), other chipsets, a logical circuit, and/or adata processing apparatus. The memory 720 may include a read-only memory(ROM), a random access memory (RAM), a flash memory, a memory card, astorage medium, and/or other storage apparatuses. The communication unitmay include a baseband circuit for processing a wireless signal. Whenthe embodiment is implemented by software, the above-mentioned techniquemay be implemented by a module (a process, a function, or the like) thatperforms the above-mentioned function.

The module may be stored in the memory and be executed by the processor.The memory may be located inside or outside the processor and may beconnected to the processor by a well-known unit.

The output unit (display unit or display unit) is controlled by aprocessor and outputs information output from the processor togetherwith a key input signal generated from the key input unit and variousinformation signals from the processor.

Further, for convenience of description, the drawings are divided anddescribed, but it can be designed to implement a new embodiment bycombining the embodiments described in each drawing. According to theneeds of those skilled in the art, it is also within the scope of thepresent invention to design a computer-readable recording medium havingrecorded thereon a program for executing the embodiments describedabove.

The method for transmitting and receiving a reference signal accordingto the present specification is not limited to the configuration andmethod of the embodiments described as described above, but all or partof each embodiment may be selectively combined and configured so thatthe above embodiments can be variously modified.

On the other hand, the method for transmitting and receiving a referencesignal of the present specification can be implemented as aprocessor-readable code on a processor-readable recording mediumprovided in the network device. The computer readable recording mediummay include all kinds of recording apparatuses in which data that may beread by the processor are stored. An example of the processor-readablerecording medium may include ROM, RAM, CD-ROM, a magnetic tape, a floppydisk, an optical data striate, or the like, and also include mediaimplemented in a form of a carrier wave such as transmission through theInternet. In addition, the processor-readable recording medium may bedistributed in computer systems connected to each other through anetwork, such that the processor-readable codes may be stored andexecuted in a distributed scheme.

Although the preferred exemplary embodiments of the present disclosurehave been disclosed for illustrative purposes, those skilled in the artwill appreciate that various modifications, additions and substitutionsare possible, without departing from the scope and spirit of thedisclosure as disclosed in the accompanying claims. Accordingly, suchmodifications, additions and substitutions should also be understood tofall within the scope of the present disclosure.

In this specification, both the object invention and the methodinvention are described, and the descriptions of both inventions can besupplementally applied as needed.

INDUSTRIAL APPLICABILITY

In the wireless communication system of the present invention, the RRCconnection method has been described with reference to an exampleapplied to the 3GPP LTE/LTE-A system, but the RRC connection method maybe applied to various wireless communication systems in addition to the3GPP LTE/LTE-A system

1. A method for performing, user equipment (UE), to decode data in awireless communication system, comprising: receiving a demodulationreference signal (DMRS) configured by a base station according to aspecific pattern from the base station through a DMRS symbol, whereinthe demodulation reference signal being transmitted on a specificantenna port and located on the same one or two time-axis symbols as atleast one other demodulation reference signal transmitted on anotherantenna port, wherein the demodulation reference signal being mapped tothe one or two time-axis symbols using at least one of a first codedivision multiplexing (CDM) on a frequency axis or a second CDM on atime axis, and wherein the specific pattern being determined accordingto characteristics of a frequency band in which the demodulationreference signal is transmitted; and decoding the data using thedemodulation reference signal.
 2. The method of claim 1, wherein thedemodulation reference signal is located on the one or two time-axissymbols based on at least one of the number of transport layers, a portindex, a rank, or the maximum number of transport ports.
 3. The methodof claim 1, wherein when the demodulation reference signal is located onone time-axis symbol, the demodulation reference signal is mapped usingthe first CDM.
 4. The method of claim 1, wherein when the demodulationreference signal is located on two time-axis symbols, the demodulationreference signal is mapped using the second CDM.
 5. The method of claim1, further comprising: receiving a signal indicating whether to applythe second CDM from the base station, wherein, the demodulationreference signal is mapped using the first CDM and the second CDM, whenthe signal indicates that the second CDM is applied.
 6. The method ofclaim 1, further comprising: receiving a signal indicating a length ofthe first CDM from the base station when the first CDM is applied,wherein it is determined whether to apply the second CDM depending onthe length of the first CDM.
 7. The method of claim 1, wherein when thedemodulation reference signal is mapped using the first CDM and thesecond CDM, a type of orthogonal cover codes (OCCs) applied to thesecond CDM is limited to at least one type by the base station.
 8. Themethod of claim 1, wherein when a phase tracking reference signal (PTRS)is transmitted, the demodulation reference signal is mapped to the oneor two time-axis symbols through the first code division multiplexing(CDM).
 9. User equipment (UE) decoding data in a wireless communicationsystem, comprising: a radio frequency unit configured to transmit andreceive a radio signal to and from the outside; and a processorconfigured to functionally coupled to the radio frequency unit, whereinthe processor receives a demodulation reference signal (DMRS) configuredby a base station according to a specific pattern from the base stationthrough a DMRS symbol, wherein the demodulation reference signal beingtransmitted on a specific antenna port and located on the same one ortwo time-axis symbols as at least one other demodulation referencesignal transmitted on another antenna port, wherein the demodulationreference signal being mapped to the one or two time-axis symbols usingat least one of a first code division multiplexing (CDM) on a frequencyaxis or a second CDM on a time axis, and wherein the specific patternbeing determined according to characteristics of a frequency band inwhich the demodulation reference signal is transmitted, and decodes thedata using the demodulation reference signal.
 10. The user equipment ofclaim 9, wherein the demodulation reference signal is located on the oneor two time axis symbols based on at least one of the number oftransport layers, a port index, a rank, or the maximum number oftransport ports.
 11. The user equipment of claim 9, wherein when thedemodulation reference signal is located on one time-axis symbol, thedemodulation reference signal is mapped using the first CDM.
 12. Theuser equipment of claim 9, wherein when the demodulation referencesignal is located on two time-axis symbols, the demodulation referencesignal is mapped using the second CDM.
 13. The user equipment of claim9, wherein the processor receives a signal indicating whether to applythe second CDM from the base station, and when the signal indicates thatthe second CDM is applied, wherein the demodulation reference signal ismapped using the first CDM and the second CDM.
 14. The user equipment ofclaim 9, wherein a signal indicating a length of the first CDM isreceived from the base station when the first CDM is applied, andwherein whether the second CDM is applied depends on the length of thefirst CDM.
 15. The user equipment of claim 9, wherein when thedemodulation reference signal is mapped using the first CDM and thesecond CDM, a type of orthogonal cover codes (OCCs) applied to thesecond CDM is limited to at least one type by the base station.
 16. Themethod of claim 9, wherein when a phase tracking reference signal (PTRS)is transmitted, the demodulation reference signal is mapped to the oneor two time-axis symbols through the first code division multiplexing(CDM).